Ballast disconnect device having a coating of flux material



Feb 2, 1965 J. G. BARAN r-:TAL 3,168,532

BALLAST DISCONNECT DEVICE HAVING A COATING OF FLUX MATERIAL Filed Oct. 3l, 1951 Fig. 1

Fig. 2

10 14 o 14 L W f;ei:f:112:3sgrgizizgsssfzizfzizggzge:

Fig. 3

INVEN TORS Joseph 6, Baran- Y A111611 E. Fei/merg United States Patent O 3,168,632 BALLAST DISCONNECT DEVICE HAVING A COATING F FLUX MATERIAL Joseph G. Baran, Northbrook, and Albert E. Feinberg, Chicago, Ill., assignors to Advance Transformer Co., Chicago, Ill., a corporation of Illinois Filed Oct. 31, 1961, Ser. No. 148,918 4 Claims. (Cl. 20G-131) This invention relates generally to thermal disconnect means for electrical circuits and more specifically is directed to a particular type of thermal disconnect means for use especially in connection with ballasts for gaseous discharge devices.

The thermal disconnect means with which this invention is concerned differs from the fuse intended to break an electrical circuit in at least two ways. It differs in one respect in that the primary protection sought is different and in another respect, in the manner in which the thermal disconnect operates.

A ballast for gaseous discharge devices usually consists of an iron core transformer with a plurality of windings thereon in circuit with one or more condensers assembled in a metal canister, immersed in a potting compound and provided with leads extending out through the canister to enable the ballast to be connected in circuit with one or more gaseous discharge devices such as, for example, fluorescent lamps.

The power requirements of the majority of uorescent lamps in use today is quite high with the consequence that ballasts must be constructed to handle substantial iiows of current. The nature of most modern ballast circuits is such that the transformer involved is made deliberately inefficient, that is, with high leakage reactance. Accompanying the inefficiency of a high leakage reactance transformer are the usual iron and copper losses manifest in heat, and these losses are somewhat increased in high powered ballasts.

The ballast is normally mounted upon metal surfaces of a fluorescent lamp fixture, it being intended that the metal surfaces will assist in conducting heat from the ballast, but its dithcult to build a ballast whose design is so universal as to provide maximum heat conduction and eiciency in any kind of xture with which the ballast may be associated. Furthermore, conditions of operation vary from installation to installation and situations may occur in spite of ordinary quality control which cause the temperature of the ballast to rise above normal.

The base for most potting compounds is a mixture of various petroleum residues such as asphalt, with silica in different proportions, providing an amorphous mass readily rendered fluid by heat. This is to enable the canisters to be easly potted during the construction thereof. Upon cooling, the compound will harden to prevent shifting of the components within the ballast. The compound will conduct the heat from the components to the walls of the canister and thence to the surfaces upon which the ballast is mounted.

When the temperature of the ballast exceeds 100 degrees centigrade, the potting compound commences to soften and if the temperature is permitted to rise above approximately 120 degrees centigrade, the potting compound will become so iiuid as to commence ilowing through the joints and lead openings of the cannister. Obviously, expensive fluorescent lamp fixtures would be ruined by the leaking of such potting compound, not to mention the dangers occasioned by the dripping and flowing of such compound to machinery, tables, merchandise, equipment and personnel located beneath the said fixtures. While it is unlikely that tire could result from the dripping potting compound, the hazard of destruction, and danger to personnel is still present.

One may deduce from the discussion above that the source of heat generated within a ballast is not necessarily a function of the amount of current drawn by the ballast but most likely is a function of the losses of the ballast and the ineliciency of heat conduction from the ballast. Since the total source of heat is the current supplied by the source of power, it is obvious that if a ballast is disconnected from its source of power, the ballast will cool and the viscosity of the potting compound will increase. A thermal disconnect device which is connected in one of the line leads and which is responsive to the temperature within the ballast will thereby serve the useful purpose of opening the line if the temperature within the ballast rises to undesirable values. Such a disconnect device may be of a replaceable type or may be permanently built into the ballast so that the operation of the thermal disconnect device renders the ballast completely useless. in any event, the operation of the thermal disconnect device will prevent melting of the potting compound within the ballast with its attendant undesirable result.

It will be seen from the above discussion that it is not intended that the thermal disconnect device operate when the circuit serving the ballast is overloaded (although it probably will do so) but rather that it operate to cause a disconnection on the basis of the temperature within the ballast, even though the actual current drawn by the ballast does not exceed its rated value. The thermal disconnect device therefore is not intended to operate due to the heating up of the conducting member thereof because of passages of large amounts of current, but rather due to a melting of the conducting member caused by external heat. Furthermore, the temperature at which the conduction member or link of the thermal disconnect device melts is reached gradually in the environment it is placed according to the invention whereas in the case of the ordinary fuse, the temperature rises so rapidly in the case of overload that the fuse link practically explodes.

The desirability of thermal disconnect devices in ballasts has been known, but so far as we are aware, there has been no satisfactory solution to the desired problem. Most thermal disconnect devices are associated permanently with ballasts since the reason for increase in the temperature of the ballast is usually caused by construction faults of the ballast and hence the ballast is just as well discarded. In such cases a short link of low melting point metal or metal alloy is located within a cartridge or container and connected in a lead that will disconnect the line if the link opens. The cartridge is physically disposed adjacent the most likely spot that will heat up usually the transformer. Such metals that are usable come generally into the category of solders which melt between and 130 centigrade. Various combinations of bismuth, lead, tin, cadmium and indium are used. Typical proportions are from 50% to about 60% of bismuth along with 30% to 50% of lead and 15% to 20% of tin. Indium is used in much smaller percentages and in alloys whose melting points are of a higher range. One alloy of 56% bismuth, 3% indium and 42% lead melted between 120 and 125 degrees centigrade: All percentages are given in weight.

There are many other combinations of low melting point metals which are suitable but it has been found in the past that these links which are intended to melt at approximately to 125 centigrade are not reliable.

The primary object of the invention is to provide a reliable thermal disconnect means intended to be used to break a circuit when the temperature of the said disconnect means rises to a value just below the melting point of potting compound in the ballast with which the disconnect means is used.

Still another object of the invention is to provide a thermal disconnect means of the character described which is highly economical, easy to manufacture and easy to install.

The -disadvantages of prior disconnect means has been that when the temperature of the metal link rises above the melting point of the metal of the link, the link tends to retain at least some semblance of its original shape which, while distorted or flattened or otherwise misshapen, nevertheless maintains an electrical connection between the lead and opposite ends of the link. We have discovered that this is brought about by the existence of a ilm of metal oxide normally contained on the surface of the link and forming a sheath-like support for the link so that the molten metal is unable to ow but, instead, is held in a mass. The oxides of the metals mentioned above do not melt until the temperature thereof reaches 600 to 800 centigrade, and by this time any potting compound contained within a ballast having such a thermal disconnect device would flow like water.

It is accordingly another object of the invention to provide thermal disconnect means in which a metal link is treated in such a manner as to remove the `oxide from the surface of the metal when the temperature of the body of the link rises above a desired value, whereby to enable the metal of the link to react to the surface tension thereof and form globules, thereby breaking up into small pieces and separating to open the circuit within which connected.

Other objects of the invention will become apparent from the specific description which follows in connection with which the drawing illustrates embodiments of the invention to aid in the explanation of the construction and operation thereof. v

In the various figures, the same reference characters are used throughout wherever feasible to designate the same or equivalent components.

FIG. l is a sectional view taken through a thermal disconnect device constructed in accordance with the invention.

FIG. 2 is a similar view, but of a modified form of the invention.

FIG. 3 is a sectional view taken through a thermal disconnect device of the prior art showing-how the link remains electrically intact when subjected to high heat.

FIG. 4 is a sectional view taken through a thermal disconnect device constructed in accordance with the invention and showing the results of heating up the link of the invention.

Basically, the invention resides in providing some means to counteract the efect of external oxide on a disconnect link formed of solder metal. The invention contemplates treating the metal in some manner with a flux such as wood rosin in some suitable forms so that as soon as the link rises in temperature, the solder is melted in the presence of the flux, thereby preventing the surface oxides from forming a non-melted tube or sheath. The surface tension of the melted solder metal causes globules or balls to be formed immediately, resulting in a complete electrical separation of the ends of the link, thereby opening the circuit being served by the link.

Referring now more specifically to the illustrations, in FIG. l there is illustrated in exaggerated dimensions, a cartridge or housing in the form of a cylindrical tube of some non-conducting material. This may be a plastic or fiber, paper or the like. Each end of the housing is closed off by means of a plug such as shown at 12, also of insulating material, and pigtail leads 14 extend from the outside of the housing 10 to the interior thereof through the plugs enabling the device to be connected into a ballast circuit.

On its interior, the leads 14 are electrically secured in any suitable manner to a metal link 16 which is formed of what may be termed solder metal. This is a low melting point alloy of any of the well known solder metals including alloys of bismuth, lead, tin, indium, cadmium and the like, there being so many of these alloys that it is impractical to specify. Any chemical or metals handbook will give various alloys and their melting points. For the purpose of protecting ballasts which are potted with asphalt type potting compounds, it is desirable to choose an alloy which will melt at temperatures of C. or less but obviously the type of potting compound and its melting point will determine the desired melting temperature of the link 16.

In the structure shown in FIG. l, the link is coated with a ux compound 18 for the purpose of dispersing or offsetting the effects of the oxide which immediately forms on 4any of the solder metals when exposed to air. The oxide may be designated 20 and is shown merely as the line between the llux coating 18 and the link 16. The compound may be a thin sheath of rosin in powder or paste form, mixed with asphalt, grease, or some other carrier material suitable.

With respect to ilux, most non-corrosive tluxes are made from mixtures of wood rosin and other materials. We have found that the preferable material with which the wood rosin is mixed to provide the iiuxing material is asphalt and in some cases grease, although the asphalt has been found to give the best results. Acid fluxes are not desirable in structures of this kind because of corrosion and We have Aalso discovered that wax mixtures do not prevent the undesirable results mentioned above.

ln FIG. 3, there is illustrated a thermal disconnect device 22 which may have a construction similar to that of the device shown in FIG. l but in which there is a link 24 of some solder material that is not provided with a fluxing medium. In such case, when the link is heated due to the rise in temperature of the ballast, the link collapses as shown and lies on the bottom of the cartridge but nevertheless in an integral member, either flattened, distorted or in some way misshapen. It will be seen that there is still a complete electrical connection between the leads 14 so that the purpose for which the thermal disconnect is thereby defeated.

In FIG. 4, on the other hand, is illustrated what occurs when a thermal disconnect device of the construction of the invention is used. As shown, When heated, the metal within the link 16 melts and as soon as it does, the linx 18 dissipates or renders ineffective the oxides on the surface of the metal, thereby permitting the clean surface molten solder to form globules such as shown at 26 and 28. r[he resulting ball formations contract and break the link into two or more pieces as shown, thus positively opening the circuit.

In FIG. 2 is illustrated another form of the invention in which the link 30 instead of being coated with the flux material 18 consists of a comminuted and reconstituted mixture of flux such as powdered rosin and the solder material.

Other forms of providing the link with uxing material will suggest themselves such as forming cores of a iiuxing material, lilling the cartridge with pastcs or fluids of uxing material, and so forth.

It is believed that the invention is sufficiently described so as to enable those skilled in this art to practice the same and construct it and it is desired to cover all modifications within the purview and scope of the claims appended hereto.

What it is desired to secure by Letters Patent of the United States is:

l. Ina ballast which is energized from a source of A.C. current for igniting at least one gaseous discharge device and said ballast has an energizing circuit which is required to be opened when the operating temperature of the ballast exceeds a prescribed value, a disconnect device connected in the energizing circuit instantaneously to open said circuit when said temperature value is exceeded comprising, a solid metal link formed of solder metal material selected to melt when said temperature value is exceeded to open said circuit and having an exterior, relatively thin, sheath coating of iiuxing material in intimate contact with the link so as to dissipate oxides accumulating on perimetric surface areas of the metal link and prevent the melted metal from holding together so that said circuit will be opened instantaneously.

2. A disconnect device as claimed in claim 1 in which said lluxing material is primarily wood rosin.

3. In a ballast which is energized from a source of A.C. current for igniting at least one gaseous discharge device and said ballast has an energizing circuit which is required to be opened when the operating temperature of the ballast exceeds a prescribed value, the said ballast assembled within a canister immersed in a potting compound; thermal disconnect means electrically connected in said energizing circuit of said ballast instantaneously to open said circuit when the temperature of the ballast exceeds said temperature value comprising, a housing adapted to be installed interior of said canister, a solid metal link disposed in said housing and formed of solder metal material selected to melt when said temperature value is exceeded to open said circuit, and an exterior coating of iluxing material on the entire surface of said link in intimate Contact therewith to dissipate oxides accumulating on the exterior surface of the metal, causing said link instantaneously to separate to open said circuit upon melting of said link metal.

4. A thermal disconnect device adapted to be installed within a potted gaseous discharge ballast and adapted to be connected in the power lead of said ballast, said device comprising a cartridge having a solid metal link therein of a metal Whose melting point is below the melting point of the potting compound of said ballast, and said link having leads extending from said cartridge and connected on the interior to opposite ends of said link, said link having oxide dispersion means comprising a thin ux coating intimately associated therewith over the entire exterior surface thereof, whereby when the link melts, the oxides will be prevented from holding the melted link together.

References Cited by the Examiner UNITED STATES PATENTS 281,576 7/83 Stieringer ZOO-135 1,386,525 8/21 Oca-Balda et al. 200-124 2,557,926 6/ 51 Swain et al 20G-135 2,592,399 4/52 Edsall et al 200-135 2,645,690 7/53 Edsall et al. 20G-113 2,782,283 2/57 Schwennesen 200-113 3,119,913 1/ 64 Benander et al. 200-135 FOREIGN PATENTS 6,224 3/07 Great Britain. 147,929 9/ 31 Switzerland.

BERNARD A. GILHEANY, Primary Examiner. 

1. IN A BALLAST WHICH IS ENERGIZED FROM A SOURCE OF A.C. CURRENT FOR IGNITING AT LEAST ONE GASEOUS DISCHAGE DEVICE AND SAID BALLAST HAS AN ENERGIZING CIRCUIT WHICH IS REQUIRED TO BE OPENED WHEN THE OPERATING TEMPERATURE OF THE BALLAST EXCEEDS A PRESCRIBED VALUE, A DISCONNECT DEVICE CONNECTED IN THE ENERGIZING CIRCUIT INSTANTANEOUSLY TO OPEN SAID CIRCUIT WHEN SAID TEMPERATURE VALU IS EXCEEDED COMPRISING, A SOLID METAL LINK FORMED OF SOLDER METAL MATE- 